This application relates to a method, reagents and kits for diagnosis and targeted screening for retinoblastoma.
Retinoblastoma is a form of cancer affecting the eyes of young children. It results from mutations in the RB1 gene that lead to the loss of functional RB protein in the retinoblasts of the fetal and juvenile eye. Because the RB protein is involved in the control mechanism for proteins or peptides that promote cell division, cells lacking in functional RB protein undergo unregulated division, leading to the formation of a tumor within the eye.
The impact of the tumor within the eye depends in large part on the size of the tumor when detected. If the tumor is very large, it may be necessary to remove the eye completely. Smaller tumors may be treated with techniques such as photocoagulation, cryotherapy or radiation, making it possible to save visual function, although treatment with radiation, which is necessary in more advanced cases, increases the risk of subsequent tumor formation. It is thus very important to the prognosis of the patient to detect retinoblastoma early on. Unfortunately, retinoblastoma is not accompanied by any readily identified early symptoms, nor is there a blood test which can be routinely administered to screen for the disease. For this reason, most early detection of retinoblastoma occurs only when one member of a family has already been diagnosed as having retinoblastoma.
The accepted procedure which is currently followed after a diagnosis of retinoblastoma in one child of a family is to carefully monitor that child's siblings and first cousins during the period of significant risk, i.e., generally through about age seven. This monitoring, which involves frequent doctor visits, and frequently includes examination under anesthesia, is very costly. It would therefore be desirable to have a mechanism for determining the genetic basis for any given child's tumors, to be more fully able to assess which of the child's siblings and other relatives are actually at risk, and to permit genetic testing of potentially-at-risk individuals to limit monitoring to those actually at risk.
Mechanisms for genetic testing for retinoblastoma have been previously proposed. For example, RNase protection of the mRNA of retinoblastoma is able to detect about 70% of mutations to the RB1 gene, but is dependent on the existence of retinoblastoma tumor mRNA. Dunn et al., Science 241: 1797 (1988); Dunn et al., Mol. Cell. Biol. 9:4594 (1989). Complete sequencing of each exon might also be performed as described by Yandell et al., N. Engl. J. Med. 321: 1689 (1989), but the cost associated with this approach using existing technology is prohibitive. Because of this cost factor, it was previously suggested that the exons of the RB1 molecule could be screened using mobility differences as described in Orita et al., Proc. Nat'l Acad. Sci. U.S.A. 86: 2766 (1989) so that only those believed to contain a mutation would be sequenced. Gallie, B. L., "The Misadventures of RB1" in Causes and Consequences of Chromosomal Aberrations, pp 429-446, CRC Press (1993).
Unfortunately, despite its early promise, the use of exon screening based on mobility differences followed by selective exon sequencing has proven unreliable for providing diagnostic and targeted screening results concerning retinoblastoma. Thus, there is still no cost effective and reliable test which can be performed on individuals diagnosed with retinoblastoma and their juvenile relations to eliminate unneeded physical examinations. It is an object of the present invention to provide such a test.